This disclosure relates to the roll forming of dies used to manufacture threaded fasteners or other patterned cylindrical articles. More particularly, it relates to the apparatus and method for forming the pattern on the dies using a cold forming machine and process.
Thread forming dies used in thread rolling are universally produced using milling and grinding equipment. Such operations usually take hours to produce a die set. Also, milling and grinding produces dies having a rough surface.
Typically thread forming tooling includes a stationary die and a moveable die. The face of the moving die is planar. The face of the stationary die is contoured to provide specific areas of engagement with the blank being formed into a fastener. The die blank 50 is M-2 tool steel fully annealed having a hardness of Rockwell 20 to 30. After forming the thread pattern on the die blank, it is heat treated to a hardness of Rockwell C-60.
The die blanks are rectangular blocks of steel with die faces impressed with a thread rolling pattern. To extend useful die life, the thread rolling pattern is created on both faces of the die blank. Once a given face is worn, the die block is rotated one hundred eighty degrees (180°) to present a fresh thread forming pattern.
The root sharpness specification for dies has traditionally been driven by die manufacturing limitations. Mills and grinding wheels have a minimum capability to hold a fine tip, and as the tip to be formed on a die gets sharper, their lifespan decreases dramatically.
It has been determined that thread rolling dies may be produced by cold forming die blanks with the ridges defining the thread pattern. Disclosed is a machine and process of reduced complexity and increased speed (minutes vs. hours). The resultant thread forming die is of close tolerance and high wear resistance.
It must be understood that the cold forming of thread defining ridges on a thread rolling die as disclosed herein is merely exemplary of the capabilities of the equipment, and process disclosed. It is contemplated that the process and equipment is suitable for other uses where deforming metal to provide a pattern upon a surface is the desired result.